New report finds few health hazards, general effectiveness among top-selling insect repellents

August 11, 2013 4:00 AM

Michigan DNR

Although no single insect repellent works in every situation, a new report has identified four chemicals that have been found to provide protection against ticks, mosquitoes and other insects.

By Jacob Axelrad Pittsburgh Post-Gazette

Whether it's mosquito netting, long-sleeved shirts or bright versus dark clothing, how best to repel insects is a question that has long vexed outdoors enthusiasts.

But a new report released July 17 by the Environmental Working Group highlights four chemicals, based on available efficacy and safety data, as the top ingredients to look for in insect repellents. According to the group's "Guide To Better Bug Repellents," the best products are DEET, Picaridin, IR3535 and Oil of Lemon Eucalyptus or its synthetic derivative p-Menthane-3, 8-diol (PMD), each of which has been approved by the Environmental Protection Agency.

Although no individual product is ideal for every situation, the report says these four chemicals provide strong protection against ticks, mosquitoes and other bugs.

Of the four chemicals listed, three are synthetic and one, Oil of Lemon Eucalyptus, comes from a botanical, or plant-based, source. Because most botanical ingredients on the market are not required by the EPA to undergo registration and efficacy or safety testing, Oil of Lemon Eucalyptus was the only botanical-based source recommended in the report, said David Andrews, a lead author on the report.

"It's gone through the full EPA registration for being a bug repellent," he said. "That's important because that means you have to provide efficacy data."

While consumers may dislike the smell and greasy texture of DEET, the most widely known chemical in bug repellents, there have been few instances of health issues when it is applied sparingly, though the report mentions rare examples when high doses have led to nervous system impairment.

"The risk of health effects with DEET tend to be very small," Andrews said. Still, "Consumers want to avoid higher concentrations."

The report's findings seem to reflect local retail trends. The two most commonly sold brands of insect repellents at REI on Pittsburgh's South Side are Sawyer, made with Picaridin, and Ben's, made with DEET, according to a local REI representative.

And yet, some studies have shown that certain insects are unaffected or can become unaffected by DEET. According to a February study conducted at the London School of Hygiene and Tropical Medicine, mosquitoes were shown to become desensitized to the chemical three hours after exposure.

Other studies have shown that factors such as blood type, increased perspiration, higher body temperatures and even the amount of beer you drink can make you more attractive to mosquitoes, according to a July article from Smithsonian magazine.

This comes at a time when insect-borne illnesses such as Lyme disease and West Nile virus are on the rise. Lyme disease, the most common vector-borne illness in the United States, has "more than doubled over the last 15 years, with more than 24,000 confirmed reports in 2011," the latest year on record, according to the report. Concentrated primarily in the American Northeast and Upper Midwest, there were 4,700 confirmed cases of Lyme disease in 2011 in Pennsylvania, according to the Centers for Disease Control and Prevention.

West Nile virus, meanwhile, saw a marked uptick from 712 cases in 2011 to 5,600 cases and 286 deaths in 2012, concentrated heavily in Dallas, Texas. Between 1999 and 2012, 1,549 people died from West Nile, according to the CDC.

"West Nile virus is here to stay," said Joe Conlon, technical adviser and expert at the American Mosquito Control Association. "It's not going away."

Since the disease is relatively new, "there's still a lot about it that we don't know," he said, adding that there is no way to predict where it will crop up. Years with few reported cases should not be taken as an indication that the virus has disappeared, he said.

"If you have a year when you don't see West Nile virus, it just means that it's lying dormant. It hasn't gone away," he said.

Conlon said people should also be wary of Eastern equine encephalitis, transmitted to humans through infected mosquitoes. Although rare, it has a 33 percent mortality rate and can cause severe brain damage to survivors, according to the CDC.

"Those it does not kill, it leaves in a vegetable state," Conlon said.

Last month, the Asian Tiger mosquito, originally from Japan, was discovered in Lawrenceville. The mosquito has been known to spread such diseases as West Nile virus, dengue fever and the dog heartworm virus.

But repellents should not be the first choice against such illnesses, according to the report.

"Repellents are just an add on," said Bill Todaro, an entomologist with the Allegheny County Health Department. "If you're in an area where you're getting bit, clothing is your first defense."

Tucking pants into socks and wearing long-sleeve shirts go a long way toward preventing insect bites. And targeting environments attractive to insects, such as stagnant water, can be very effective, he said.

"You get rid of that, you get rid of the problem," he said.

When repellents are used, according to the report, they should be applied in moderation, bearing in mind that no single repellent works well all the time. Consumers should not use anything higher than a 30 percent concentration of DEET as this is all that is necessary, the report states.

"Anything more would be overkill," Conlon said.

Mosquito-borne diseases were once quite common in the United States. But because county health departments conduct routine mosquito control operations, effectively eliminating the pest, it can be easy to forget the severity of such illnesses as yellow fever and dengue fever, Conlon said.

He advised what he called the "three Ds" for mosquito prevention: drain standing water, dress in long pants and long sleeves, preferably lighter colors, and defend -- using EPA-registered repellents.

"We don't want people to get complacent," he said. "Because complacency kills."